Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$65.56	10.619%	$72.5218	$72.52	$72.50	$72.50
Purchase #2	$152.68	10.303%	$168.4106	$168.41	$168.40	$168.40
Purchase #3	$203.40	13.523%	$230.9058	$230.91	$230.90	$230.90
Purchase #4	$170.62	4.375%	$178.0846	$178.08	$178.10	$178.10
Purchase #5	$244.55	12.383%	$274.8326	$274.83	$274.85	$274.80
Purchase #6	$178.87	11.581%	$199.5849	$199.58	$199.60	$199.60
Purchase #7	$139.30	12.596%	$156.8462	$156.85	$156.85	$156.80
7 purchase totals =	$1,154.98		$1,281.1865	$1,281.18	$1,281.20	$1,281.10